In master cylinders as defined above, the seal, also known as an isolation seal or sealing cup, can be mounted in reverse in its groove, which will not become apparent until the brakes are used, which presents a grave risk and requires the replacement of the master cylinder.
In the case of a simple master cylinder, there is only one supply chamber bordered by the resupply seal and seal, the first being placed behind the second in the direction of movement of the master-cylinder piston when actuated by the brake pedal. In the case of a tandem master cylinder, there are two pistons that operate in combination, each piston cooperating with a supply chamber and a pressure chamber.
The risk of reversed assembly, therefore, exists for both seals.